High-potency animal feeds, as they are normally used today in intensive animal raising, contain a number of additives of prophylactic and/or nutritive effect. These include, among others, antibiotics and enzymes. While the use of antibiotics has found acceptance in mixed feeds of all kinds, enzymes are not as yet used on a large scale in the field.
Thus, U.S. Pat. No. 3,017,272 suggests the use of from 1 to 200 ppm of Virginiamycin in feeds, U.S. Pat. No. 2,809,892 suggests the use of from 1 to 25 ppm of zinc Bacitracin in feeds, U.S. Pat. No. 4,062,732 suggests the use of certain acid proteases in feed, and U.S. Pat. No. 3,455,696 suggests the use of procaine penicillin, dehydrostreptomycin or tetracycline and an acid protease in feeds.
The feed mixtures used in modern intensive animal raising programs are generally optimized in all nutrient components to the extent that further improvement does not seem readily possible.